$$\int\frac{e^{x}}{1-e^{3x}}dx$$
$\frac{2\sqrt{3}\arctan(\frac{\sqrt{3}\left(2e^{x}+1\right)}{3})+\ln(e^{x}+e^{2x}+1)-2\ln(|e^{x}-1|)}{6}+С$
$-\frac{e^{x}}{e^{3x}-1}$
